Electronic display tubes



Filed April 30, 1965 ELECTRON BEAH SOURCE INVENTOR WILLIAM P. KRUGER a-c- Swixk ATTORNEY 3,395,309 ELECTRONIC DISPLAY TUBES William P. Kruger, Los Altos Hills, Califl, assignor to Hewlett-Packard Company, Palo Alto, Calif., a corporation of California Filed Apr. 30, 1965, Ser. No. 452,178 5 Claims. (Cl. 315-13) ABSTRACT OF THE DISCLOSURE It is an object of the present invention to provide a cathode ray tube having a source of low energy electrons disposed near the exit of the main electron beam deflection system for uniformly illuminating the display screen.

It is another object of the present invention to provide an improved cathode ray display tube having improved apparatus for uniformly illuminating the display screen.

In accordance with the illustrated embodiments of the present invention, a filament is disposed behind a conductive mesh grid at the entrance of the post-accelerator region of thetube. A small potential diflference between the filament and the mesh grid causes small quantities of low energy electrons to migrate through the mesh grid and be accelerated toward the display screen with random trajectories. These electrons uniformly bombard the phosphors which comprise the display screen and cause it to emit light at an intensity which is cont-rolled by the filament current.

These and other objects of the present invention will be apparent from a reading of this specification and an inspection of the accompanying drawing which shows a pictorial diagram of a cathode ray tube having a postaccelerator region and showing the source of low energy electrons for illuminating the display screen according to the present invention.

Referring now to the drawing, there is shown a cathode ray tube including an electron beam source 9 and beam deflectors 11 disposed within an evacuated envelope 13 with a display screen 15 disposed at the end of the envelope remote from the beam source. Intermediate the beam deflectors and the display screen is a post-acceleration region including a source of voltage 17 connected to a divider 19 for establishing a potential gradient along the axis 21 of the tube, as shown by equipotential lines 23. A fine mesh grid 25 of hemispherical shape is disposed along the axis 21 of the tube at the entrance of the post-accelerator region to establish an equipotential surface at a reference or ground potential. The cylindrical support structure 27 for the mesh grid 25 includes an inwardly extending flange 28 at the beam entrance end which supports a magnetic shield tube 29 for the filament wires 31. Voltage source 33 supplies current to the filament 35 through an adjustatble resistor 37 which thus controls the operating temperature of the filament 35.

ted States Patent v 3,395,309 Patented July 30, 1968 The potential gradient established between the filament 35 and the mesh grid 25 by voltage source 39 causes low energy electrons emitted by filament 35 to migrate toward the mesh grid 25 and then pass therethrough into the postaccelerator region. The potential gradient in this region accelerates the low energy electrons along radii 41 of the field toward the display screen 15 where they excite the phosphors to emit light uniformly over the area of the display screen 15. The uniformity of illumination may be controlled by the repeller grid 43 disposed near the filament 35. This grid operates at a variable low negative potential with respect to the filament provided by source 45 for altering the pattern of movement of the electrons from filament 35 toward the mesh grid 25. The uniformity of the screen illumination may thus be controlled by varying the potential of source 45 connected between the grid 43 and the filament 35.

The apparatus of the present invention thus provides an improved source of low energy electrons for uniformly illuminating the display screen of a cathode ray tube with an intensity that is readily controllable over a wide range.

I claim:

1. Cathode-ray tube apparatus for providing an illuminated display screen, the apparatus comprising:

electron beam producing means disposed within an evacuated envelope near one end thereof;

a display screen disposed away from said beam producing means at an end of said envelope for receiving said electron beam to produce a visual display thereof;

a mesh grid interposed between said beam producing means and said display screen along a normal path of the electron beam;

a post accelerator region between said mesh grid and said display screen including means producing a potential gradient along the normal path of the electron beam in a direction to accelerate electrons to ward the display screen; and

a source of electrons disposed on the side of said mesh grid remote from the display screen and away from the normal path of the electron beam for supplying electrons in a direction through said mesh grid and into said post accelerator region.

2. Cathode-ray tube apparatus as in claim 1 comprismeans connected to said source of electrons and said mesh grid for establishing a difference of potential therebetween with said mesh grid more positive than said source.

3. Cathode-ray tube apparatus as in claim 2 comprising:

a deflection electrode near said source of electrons on the side thereof remote from the normal path of the electron beam; and

means connected to said deflection electrode to establish a difference of potential with respect to said source of electrons for deflecting said electrons toward said normal path.

4. Cathode-ray tube apparatus as in claim 3 comprising:

a magnetic shield within said envelope disposed about connections to said source of electrons and to said deflection electrode on the side of said mesh grid remote from said display screen.

3 4 5. Cathode-ray tube apparatus as in claim 1 whereinz .4 l References Cited said means producing a potential gradient in the post- UNITED STATES PATENTS accelerator region includes an electrode disposed away from and along the normal path of the elec- 2,100,704 11/1937 Arden 315fl17 tron beam having terminals connected to said elec- 5 2,798,185 7/1957 Hansen et 31513 trode at spaced locations along the length thereof; 3,188,508 6/1965 Thomas 315-13 X 3,325,673 6/1967 Anderson 313-71 X and a source of potential connected to said terminals for p I producing a gradient of potential drop along the RODNEY D BENNETT Primary length of said electrode. 10 M. F. HUBLER, Assistant Examiner. 

